Generic dispensing devices are known from the prior art. It is provided in the case of such devices that medium is dispensed from a medium reservoir by means of a pump device or another conveying device through the outlet opening to an environment. This serves in particular to dispense pharmaceuticals and cosmetics. The dispensing operation reduces the amount of medium in the medium reservoir. To prevent a negative pressure forming in the medium reservoir as a result, which is a hindrance to further dispensing operations, generic dispensing devices have an inlet opening through which air can flow into the dispensing device and into the medium reservoir where it remains for replacement of the dispensed medium and leads to a pressure equalization.
What is problematic here is that the inlet opening and the connection of the inlet opening to the medium reservoir permit an escape of the medium in gaseous form. If therefore the dispensing device is kept in storage for a lengthy period, a relevant quantity of the medium can escape through the inlet opening. Not only is this is a problem due to the loss of the medium in itself, but additionally it results in the concentration of active substances remaining in the medium reservoir being altered, so that the dosage in accordance with the intended purpose is no longer assured during dispensing.